What does "!" (exclamation mark) means in http header "Cache-Control: !no-store, !bypass-cache"?

Question

I noticed that the page http://www.r7.com has the following http reponse header:

Cache-Control:!no-store,!bypass-cache,max-age=22s

What does the "!" exclamation mark character mean? Is that a negated expression?

Answer 1

The specification for Cache-Control (RFC 7234) doesn't include any exclamation marks.

This is unspecified behaviour. Only the operators of that website know what they mean, but general clients are unlikely to support it.